This invention relates generally to detergent compositions and cleaning compositions having enhanced detergency and cleaning capabilities. It relates more particularly to detergent and cleaning compositions containing the 2-tolyl isomer of linear alkyltoluene sulfonates in concentrations higher than were previously available in the prior art, owing to the discovery of the revolutionary catalyst and process for producing such isomers in high concentration, as detailed herein. According to a preferred form of the invention, an alkylated benzene, such as toluene or ethylbenzene, are utilized as an aromatic compound that is further alkylated and sulfonated to provide a surfactant useful in detergent formulizations.
Chemical compounds useful for removing grease, oils, dirt and other foreign matter from various surfaces and objects have been known for some time, including the simple soaps which are manufactured by the saponification of oils (including animal fats and vegetable oils). Saponification is essentially a process whereby aqueous alkali metal hydroxide is mixed with an ester (such as an animal fat or vegetable oil) to cause de-esterification of the ester with the formation of the alkali salt(s) of the carboxylic acid(s) from which the ester was derived, which salt(s) are typically very soluble in aqueous media. Importantly, the anion portions of such alkali salts of the carboxylic acid(s) include as part of their molecular structure a hydrophilic portion, i.e., the carboxylate function, which is highly attracted to water molecules. Such salts also include a hydrophobic portion as part of their molecular structure, which is typically a hydrocarbon-based portion containing between about 12 and 22 carbon atoms per molecule. Such salts are commonly referred to by those skilled in the art as “salts of fatty acids”, and by laypersons as “soap”. Aqueous solutions of salts of fatty acids are very effective at causing grease, oils, and other normally water-insoluble materials to become soluble and thus capable of being rinsed away, thus leaving behind a clean substrate which may typically comprise a tabletop, countertop, article of glassware or dinnerware, flatware, clothing, architecture, motor vehicle, human skin, human hair, etc.
While the industries for the production of such soaps from fats and oils are well-established, saponification chemists and other workers have continuously sought improved chemistry for rendering materials which are not normally soluble in aqueous media to become soluble therein. Towards this end, a wide variety of materials have been identified by those skilled in the art, with the common denominator of such materials being that the materials all contain a hydrophobic portion and a hydrophilic portion in their molecular structures.
One family of materials that have been identified as suitable soap substitutes are the linear alkylbenzene sulfonates (“LAB sulfonates”). The LAB sulfonates in general are exemplified as comprising a benzene ring structure having a hydrocarbyl substituent (or “alkyl substituent”) and a sulfonate group bonded to the ring in the para position with respect to one another. The length of the hydrocarbon chain of the alkyl substituent on the ring is selected to provide a high level of detergency characteristics while the linearity of the hydrocarbon chain enhances the biodegradability characteristics of the LAB sulfonate. The hydrocarbyl substituent may typically contain 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15 carbon atoms (the “detergent range”) in a substantially linear arrangement, and may be attached to the benzene ring by means of a conventional Friedel-Crafts alkylation process using a corresponding olefin and employing a Lewis acid catalyst such as aluminum chloride and conditions known to those skilled in the art as useful for such alkylations. Various alkylation processes useful for production of alkylbenzenes are described in U.S. Pat. Nos. 3,342,888; 3,478,118; 3,631,123; 4,072,730; 4,301,316; 4,301,317; 4,467,128; 4,503,277; 4,783,567; 4,891,466; 4,962,256; 5,012,021; 5,196,574; 5,302,732; 5,344,997; and 5,574,198, as well as European patent application 353813 and Russian patent 739,046, the entire contents of which are incorporated herein by reference thereto.
Once a hydrocarbyl radical has been appended to a benzene ring in accordance with the foregoing, the resulting linear alkylbenzene must subsequently be sulfonated in order to produce a finished detergent material that is capable of solubilizing grease, oils, dirt, and the like from various substrates, such as dishes, motorized vehicles, hard surfaces, architecture, and fabrics, to name but a few. Sulfonation is a known chemical process whose reactants and conditions are known to those skilled in the chemical arts. Through the process of sulfonation, a sulfonate group is caused to become chemically bonded to a carbon atom in the benzene ring structure of the linear alkylbenzene, thus providing the molecule as a whole with a hydrophilic sulfonate group in addition to the hydrophobic hydrocarbyl portion.
It is known that during the course of mono-alkylation of the benzene ring to introduce a hydrocarbon tail into the molecular structure, several structural isomers are possible in which the benzene ring is attached to various points along the hydrocarbon chain used. It is generally believed that steric effects of the mono-olefin employed play a role in the distribution of isomers in the mono-alkylated product, in addition to the catalyst characteristics and reaction conditions. Thus, it is possible for a single benzene ring to become attached to, say, the 2, 3, 4, or 5 positions in a 10 carbon atom linear mono-olefin, with a different alkylbenzene isomer being produced in each such case. Sulfonation of such different materials results in as many different alkylbenzene sulfonates, each of which have different solubilization capabilities with respect to various oils, grease, and dirt, etc.
The sulfonates of the 2-phenyl alkyl isomers are regarded by those skilled in the art as being very highly desirable materials, as sulfonated linear alkylbenzene detergent materials made from sulfonation of the 2-phenyl alkyl materials have superior cleaning and detergency powers with respect to the sulfonation products of other isomers produced during the alkylation. This is believed to be due in part to the greater degree of separation of the hydrophobic and hydrophilic portions of the molecule in the 2-phenyl isomer than in the other isomers present. The most desired 2-phenyl alkyl isomer products may be represented structurally, in the case of the alkylbenzenes, as: which in a preferred embodiment has n equal to any integer selected from the group consisting of: 5, 6, 7, 8, 9, 10, 11, and 12. Since the Friedel-Crafts type alkylation employed to produce 2-phenyl alkyl isomers according to the invention may often utilize a mixture of olefins in the detergent range (C8 to C15), a distribution of various alkylbenzenes results from such alkylation.
These same considerations as above relating to linear alkylbenzenes are also applicable to the linear alkyltoluenes of this invention. The present invention is therefore in one broad respect concerned with the use of sulfonated 2-toluyl alkyltoluenes derived from the alkylation of toluene, preferably using olefins having a carbon number distribution in the detergent range, in detergent formulations.
In the case of benzene alkylation using a detergent range olefin, a 2-phenyl alkylbenzene is but one possible structural isomer resulting from the alkylation of benzene with an olefin, and a mixture of 2-phenyl alkylbenzenes results from the alkylation of benzene using as reactants a feed which includes a mixture of olefins in the detergent range. This may be due to resonance stabilization which permits effective movement of the double bond in an activated olefin/Lewis acid complex. Generally speaking, the collection of all isomeric products produced from the alkylation of benzene with a mixture of olefins in the detergent range is commonly referred to by those of ordinary skill in the art as “linear alkylbenzenes”, or “LAB's”. Frequently, those skilled in the art use “linear alkylbenzenes” or “LAB's” interchangeably with their sulfonates. It is common for people to say LAB's when they are actually referring to sulfonated LAB's useful as detergents. These same considerations apply to linear alkyltoluenes as well, and linear alkyltoluenes may be referred to as “LAT's”.
Typically, LAB's are manufactured commercially using classic Friedal-Crafts chemistry, employing catalysts such as aluminum chloride, or using strong acid catalysts such as hydrogen fluoride, for example, to alkylate benzene with olefins. While such methods produce high conversions, the selectivity to the 2-phenyl isomer in such reactions as known in the prior art is low, generally being about 30% or less. LAB's with a high percentage of the 2-phenyl isomer are highly desired because such compounds when sulfonated have long “tails” which provide enhanced solubility and detergent properties.
While the alkylation of benzene to provide alkylbenzenes that are further sulfonated to afford surfactants has served the industry well for decades, there are disadvantages associated with the use of benzene. For example, benzene is a toxic material which requires specialized equipment for its safe handling, and which is traded under stringent regulation by various governmental bodies. Thus, mere handling and health aspects have provided a motivation for chemists to seek alternative surfactants which are effective, but are not based on benzene.
Further, the price of benzene is generally higher than other aromatic compounds which may be suitable candidates from which surfactants may ultimately be derived, such as toluene and ethylbenzene.
One of the most important aspects of a surfactant that is intended to be utilized in aqueous solution is its solubility. Formulations need good solubility in order to perform well. As mentioned, surfactant molecules generally comprise a hydrophobic portion and a hydrophilic portion. As the hydrophobic group increases in molecular weight (the hydrophilic group being held the same), the surfactant becomes less soluble in water. Similarly, for the same hydrophobic group, the surfactant becomes more water soluble as the hydrophilic group becomes more water soluble.
Surfactants exhibit behavioral characteristics which differ from those exhibited by most other organic molecules. The solubility of most chemical compounds in water increases as the temperature of the water is increased. The solubility of ionic surfactants increases dramatically above a certain temperature known as the Krafft point. When the solubility of an ionic surfactant is plotted against temperature, a complex graph results. The solubility slowly increases as the temperature rises up to the Krafft temperature, after which there is seen a very rapid rise in solubility with only moderate increases in temperature, and it is at the Krafft temperature at which micelles are formed. Below the Krafft temperature, solubility is limited as no micelles are formed. Thus, a surfactant having a Krafft temperature that is above the temperature at which the surfactant is intended to be used will not have sufficient solubility at the use temperature to be effective as a surfactant.
Thus, providing a surfactant material having an sufficiently high Krafft temperature to enable its use at ordinary temperatures, and which surfactant is not benzene-derived, represents a very desirable goal. To provide such a material having higher 2-phenyl isomer content over that available in the art so as to increase its detergency characteristics would be a huge step forward in the art of detergents.